JP7428465B2 - Red phosphor and light emitting device - Google Patents

Description

The present invention relates to a red phosphor for an LED (Light Emitting Diode) or an LD (Laser Diode), and a light emitting device using this red phosphor. More specifically, the present invention relates to a red phosphor with high brightness and a light emitting device with excellent brightness using the red phosphor.

A white LED is a device that emits pseudo white light by combining a semiconductor light emitting element and a phosphor, and a typical example thereof is a combination of a blue LED and a YAG yellow phosphor. However, although this type of white LED falls within the white range in terms of its chromaticity coordinate values, it lacks a red light emitting component, so it has a low color rendering property for lighting applications, and is used in image display devices such as liquid crystal backlights. However, there is a problem with poor color reproducibility. Therefore, in order to compensate for the insufficient red light emitting component, it has been proposed to use a nitride or oxynitride phosphor that emits red light together with the YAG phosphor (Patent Document 1).

Nitride phosphors that emit red light are known to have an inorganic compound having the same crystal structure as the CaAlSiN ₃ crystal phase as a host crystal activated with optically active elements ^. CaAlSiN ₃ phosphor is said to emit light with particularly high brightness (Patent Document 2). Further, this document describes that by substituting a part of Ca with Sr, a phosphor whose emission peak wavelength is shifted to the shorter wavelength side can be obtained. This Eu ²⁺ -activated (Sr,Ca)AlSiN ₃ phosphor has a shorter emission wavelength than the CaAlSiN ₃ nitride phosphor and increases the spectral components in the region with high visibility, so it is suitable for use in high-brightness white LEDs. Effective as a red phosphor.

In recent years, in order to further increase the brightness of lighting devices and backlight devices, many studies have been made to increase the brightness of phosphors. For example, there is knowledge that β-type Sialon phosphor, which is a divalent europium-activated oxynitride green-emitting phosphor, can exhibit excellent fluorescence characteristics by controlling the absorption rate when excited at a wavelength of 600 nm. (Patent Document 3).

On the other hand, control of light absorption in light emitting device packages fabricated using these phosphors is also being studied, and the characteristics of the package can be improved by minimizing the absorption of light other than the blue excitation light of the red phosphor. In this case, as a way to select wavelengths of light other than blue excitation light, consideration is being given to focusing on the fluorescence spectrum of phosphors other than the red phosphor used in package production ( Patent Documents 4, 5, 6). That is, it has been conventionally considered to determine the absorption rate of a red phosphor as shown in FIG. 3(b) depending on the fluorescence characteristics of a yellow phosphor as shown in FIG. 2 of Patent Document 6. .

JP2004-71726A International Publication No. 2005/052087 International Publication No. 2011/083671 JP2016-20486A Japanese Patent Application Publication No. 2012-109592 Japanese Patent Application Publication No. 2012-246462

However, in the above-mentioned conventional technology, even if an attempt was made to increase the brightness by increasing the amount of europium that activates the red phosphor, there was a problem in that the fluorescent properties could not be maintained. That is, the conventional technology has not been able to solve the problem that it is difficult to maintain both fluorescence characteristics and high brightness. For this reason, when attempting to create a light emitting device such as a white LED using a red phosphor according to the prior art, it is necessary to strictly adjust the compatibility between the characteristics of the other phosphors to be combined and the characteristics of the red phosphor to produce sufficient white light. cannot be obtained, which has been a problem in manufacturing light-emitting devices.

Therefore, in this technical field, a red phosphor that can stably provide high luminance is desired for manufacturing high-luminance light emitting devices.

As a result of intensive studies to solve the above problems, the present inventors discovered that by controlling the value of the difference in absorption rate when excited with two specific wavelengths, a red phosphor with excellent brightness can be obtained. The present invention has been accomplished.

That is, the present invention can provide the following.

(1) General formula: MAlSiN ₃ (M is one or more elements selected from Ca and Sr), a part of the M element is replaced with the Eu element, and the main crystal phase is the CaAlSiN ₃ crystal phase. Phosphors having the same structure, where the absorption rate for excitation light with a wavelength of 455 nm is a% and the absorption rate for excitation light with a wavelength of 700 nm is b%, a−b≧85.0%. .

(2) The phosphor according to (1) above, having an Eu content of 0.40 to 4.00 wt%.

(3) The phosphor according to (1) or (2) above, wherein the M element contains at least Sr.

(4) The phosphor according to any one of (1) to (3) above, wherein 85.0%≦a−b≦99.0%.

(5) A light-emitting device comprising the phosphor described in (1) to (4) above and a light-emitting element.

According to the embodiments of the present invention, it is possible to provide a CaAlSiN _{3 -based nitride red phosphor with high brightness while maintaining the fluorescent properties as a red phosphor, and when combined with a light emitting element such as an LED, it is possible to provide a CaAlSiN 3} -based nitride red phosphor with high brightness. A light emitting device can be provided. Examples of the light emitting device include a lighting device, a backlight device, an image display device, and a signal device. Further, when the red phosphor according to the present embodiment is used, especially when producing a white LED device, there is also an effect that problems in compatibility with the characteristics of other phosphors to be combined are less likely to occur.

EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing this invention is demonstrated in detail.

In this specification, unless otherwise specified, a numerical range is a range that includes its lower limit and upper limit.

The embodiment of the present invention provides a general formula: MAlSiN ₃ (M=one or more elements selected from Ca and Sr), in which a part of the M element is replaced with an Eu element, It is a red phosphor whose main crystal phase has the same structure as the CaAlSiN ₃ crystal phase. As used herein, the term "phosphor" is a concept that includes phosphor products produced by manufacturers. In this specification, the term "product" of phosphor refers to an item to be distributed, and is generally an aggregate of particles mainly composed of phosphor particles, with different phases or particles that do not affect the optical properties. It may contain impurities that are unavoidable during the manufacturing process.

In general, the skeletal structure of CaAlSiN ₃ crystal is composed of bonded (Si, Al)-N ₄ regular tetrahedra, with Ca atoms located in the gaps between them. The Ca ²⁺ site can also be replaced with a divalent cation, for example, with Sr ²⁺ . When some of the sites occupied by divalent cations represented by Ca ²⁺ are replaced with Eu ²⁺ , which acts as a luminescent center, it functions as a red phosphor.

An inorganic compound whose main crystal phase has the same crystal structure as the CaAlSiN ₃ crystal phase is one in which the powder X-ray diffraction pattern is the same as that of the CaAlSiN ₃ crystal, and the inorganic compound has a powder X-ray diffraction pattern that is the same as that of the CaAlSiN 3 crystal. Includes peak shifts due to substitution. Further, it does not necessarily have to be a single phase, and may contain a different phase as long as it does not inhibit light emission, but the amount of the different phase is preferably small, as will be described later.

The phosphor according to the embodiment of the present invention has an absorption rate of a% when excited at a wavelength of 455 nm (hereinafter abbreviated as "455 nm absorption rate") and an absorption rate of a% when excited at a wavelength of 700 nm (hereinafter referred to as "700 nm absorption rate"). When b% is the absorption rate (abbreviated as “absorption rate”), it is necessary that a−b≧85.0%. In a preferred embodiment, 85.0%≦a-b≦99.0%, more preferably 87.0%≦a-b≦99.0%, even more preferably 90.0%≦a -b≦99.0%. In some embodiments, the value of a-b may be in the range of 87.0%≦a-b≦94.0%, or 90.0%≦a-b≦94.0%. If a-b is less than 85.0%, it means that the value of a is small or the value of b is large. However, if the value of a is small, the absorption of the wavelength of 455 nm by Eu, which acts as a luminescence center. When the ratio is low and the value of b is large, the inhibition of light emission due to non-emission absorption is large, so that sufficient brightness cannot be obtained in any case. The present inventor discovered that whether or not the value of a-b is 85.0% or more affects the brightness performance of the Eu ²⁺ activated phosphor having the MAlSiN ₃ structure, and completed the present invention. It is something that That is, if the value of ab is 85.0% or more, a phosphor having a crystal structure exhibiting excellent fluorescent properties can be obtained. On the other hand, when the value of a-b is less than 85.0%, problems occur such as distortion of the crystal structure and deterioration of transparency, or a non-negligible amount of foreign phases that inhibit light emission. do.

Furthermore, in order to increase the value of a−b, it is necessary to increase the value of a, but in order to increase the value of a, it is not enough to simply increase the amount of Eu. This is because if the amount of Eu is excessive, a loss phenomenon known as concentration quenching occurs, and the brightness conversely decreases. That is, even if the amount of Eu contained in the phosphor raw material is increased, the brightness does not necessarily increase in proportion to the amount. Also, depending on the use of the phosphor, increasing the value of ab excessively may unnecessarily complicate the manufacturing method. Therefore, in a more preferred embodiment, from the viewpoint of not causing concentration quenching, suppressing non-luminous absorption, and simplifying the manufacturing method, the maximum value of a-b is set when applying the red phosphor to a light-emitting device. may be set to 99.0%.

The reason why b is defined as the 700 nm absorption rate is as follows. Since the wavelength of light that can be converted into red light by Eu ²⁺ present in CaAlSiN ₃ -based nitride phosphors that can be used in light-emitting devices is 400 nm to 700 nm, absorption in longer wavelength ranges is due to Eu ² This is absorption that does not involve emission of ⁺ , that is, absorption that does not involve emission of the host material. Here, the present inventors have focused on the fact that in the CaAlSiN ₃ -based nitride phosphor, the external quantum efficiency is low while the internal quantum efficiency tends to be high near 700 nm. If the host material has large absorption without light emission at a wavelength of 700 nm, the internal quantum efficiency is high, so the generation of photons that do not lead to light emission will increase, and energy will be wasted, which will have a negative impact on the performance as a phosphor. . Therefore, the inventors have found that by reducing the absorption at 700 nm, which is the shortest wavelength at which non-emission absorption occurs, it is possible to increase the brightness while maintaining the fluorescence characteristics of the red phosphor itself. In other words, a red phosphor that can maintain both fluorescence characteristics and high brightness based on the values of a and b, which are the characteristics of the red phosphor itself, without depending on the characteristics of other phosphors to be combined. The structure of can be determined.

In order to control the proportion of non-radiative absorption at wavelengths longer than 700 nm, it is sufficient to increase the crystallinity of the CaAlSiN ₃ -based nitride phosphor or reduce impurities and foreign phases that absorb visible light. More specifically, depending on the combination of various parameters such as the charging ratio of raw materials during manufacturing, firing conditions such as firing temperature, firing time (holding time), and firing atmosphere pressure, and the average particle size of the phosphor. By increasing the crystallinity of the phosphor and reducing impurities and foreign phases, the value of ab can be adjusted appropriately.

In addition, a is determined as the 455 nm absorption rate because 455 nm is a typical excitation wavelength for CaAlSiN ₃ -based nitride phosphors, and the absorption rate is an appropriate parameter for evaluating the brightness of the phosphor. .

The 455 nm absorption rate (a%) is calculated by calculating the number of excitation light photons (Qex) and the number of excitation reflected light photons (Qref) from the spectrum in the wavelength range of 450 to 465 nm when excited at 455 nm, and a (%) = ( It is obtained from the formula (Qex-Qref)/Qex)×100. Similarly, the wavelength of 700 nm (b%) is determined by calculating the number of excitation light photons ( ^Q'ex ) and the number of excitation reflected light photons ( ^Q'ref ) from the spectrum in the wavelength range of 695 to 710nm when excited at 700nm, and b (%)=(( ^Q'ex - ^Q'ref )/ ^Q'ex )×100.

The Eu content of the phosphor of the present invention is preferably 0.40 to 4.00 wt%, more preferably 1.00 to 4.00 wt%, even more preferably 1.60 to 3.00 wt%. be able to. Since Eu is an atom responsible for the luminescence of the phosphor, that is, the luminescence center, if its content is extremely low (for example, less than 0.40 wt%), there is a risk that the phosphor will not be able to perform its function. However, if the Eu content becomes too high (for example, over 4.00 wt%), a loss phenomenon known as concentration quenching of the phosphor occurs due to energy transfer between Eu atoms, and the brightness of the phosphor decreases. There may be a tendency for it to decrease.

The phosphor of the present invention preferably contains at least Sr. If Sr is contained, the emission wavelength will be shorter than that without Sr, and the spectral components in the region with high visibility will increase, so it is effective as a red phosphor for high-intensity white LEDs. In a preferred embodiment, the phosphor can contain both Ca and Sr, and the proportion of Sr in the M element is not particularly limited, but is preferably 35 to 45 wt%.

The method for producing the red phosphor of the present invention is not particularly limited as long as the value of a _- b can be appropriately obtained. This can be done by adjusting the manufacturing conditions so that it can be obtained.

The state of the samples produced by each manufacturing method varies depending on the raw material composition and firing conditions, such as powder, lumps, and sintered bodies. It can be made into a powder of any size. For example, when it is suitably used as a phosphor for LED, it is preferable to adjust the average particle size of the phosphor to 5 to 35 μm. If the average particle size is too large (for example, more than 35 μm), there is a problem that the dispersibility in the sealing resin becomes poor when manufacturing a white LED, resulting in lower brightness and lower manufacturing stability. sell. Furthermore, if the average particle size is too small (for example, less than 5 μm), the external quantum efficiency may decrease. Note that in this specification, the average particle size refers to the mass median diameter (D ₅₀ ). The mass median diameter can be converted and calculated from the volume median diameter obtained from a cumulative distribution curve measured by a laser diffraction scattering method, for example, according to JIS R1622:1995 and R1629:1997.

The firing temperature in the firing step in manufacturing the phosphor according to the embodiment of the present invention is not particularly limited as long as it can obtain an appropriate value of a-b, but for example, 1500°C or more and 2000°C or less, More preferably, the temperature range is 1700°C or more and 2000°C or less, and even more preferably 1700°C or more and 1950°C or less. If the firing temperature is too low (for example, less than 1500° C.), a problem may arise in which the amount of unreacted raw materials increases. Furthermore, if the firing temperature is too high (for example, over 2000°C), there is a risk that the main crystal structure (main phase) will decompose.

Further, the firing time in the firing step is not particularly limited as long as it can obtain an appropriate value of a-b, but for example, it is in the range of 1 hour to 24 hours, preferably in the range of 4 hours to 24 hours. By doing so, it is possible to reduce the amount of unreacted raw material remaining and to reduce insufficient grain growth.

Further, the pressure of the firing atmosphere in the firing step is not particularly limited as long as it can obtain an appropriate value of a−b. Generally, the higher the atmospheric pressure, the higher the decomposition temperature of the phosphor, but in consideration of industrial productivity, it is preferably less than 1 MPa.

In manufacturing the phosphor, post-treatment steps such as an acid treatment step for the purpose of removing impurities and an annealing treatment step for the purpose of improving crystallinity may be further performed.

The phosphor of the present invention can be used in a light-emitting device having a phosphor and a light-emitting element. In particular, by irradiating ultraviolet light or visible light containing a wavelength of 350 nm or more and 500 nm or less as an excitation source, light emission having a peak at a wavelength of 605 nm or more and 650 nm or less is produced. Alternatively, by further combining with a green to yellow phosphor and/or a blue phosphor, a desired luminescent color such as white light can be easily obtained.

The present invention will be further explained in detail by showing examples. However, the present invention is not limited to only the contents shown in the examples.

(Production method)
As raw materials for the phosphor of Example 1, 65.6 g of α-type silicon nitride powder (Si ₃ N ₄ , SN-E10 grade, manufactured by Ube Industries, Ltd.) and 57.6 g of aluminum nitride powder (AlN, E grade, manufactured by Tokuyama Corporation) were used. 6g of europium oxide powder (Eu ₂ O ₃ , RU grade, manufactured by Shin-Etsu Chemical Co., Ltd.) 4.9g were premixed in advance, and then kept in a nitrogen atmosphere with a moisture content of 1 mass ppm or less and an oxygen content of 1 mass ppm or less. 9.0 g of calcium nitride powder (Ca ₃ N ₂ , manufactured by Materion Co., Ltd.) and 112.9 g of strontium nitride powder (Sr ₃ N ₂ , purity 2N, manufactured by Kojundo Kagaku Kenkyusho Co., Ltd.) were added to the premixed mixture in a glove box. was further added and dry mixed to obtain a raw material mixed powder. 250.0 g of this raw material mixed powder was filled into a lidded container made of tantalum.

The container filled with the raw material mixed powder was taken out from the glove box and immediately set in an electric furnace with a carbon heater, and the inside of the furnace was sufficiently evacuated to 0.1 Pa or less. Heating was started while the furnace was being evacuated, nitrogen gas was introduced at 600° C., and the atmospheric pressure in the furnace was set to 0.9 MPa. After introducing the gas, the temperature was raised to 1950°C, and the holding temperature was 1950°C, and firing was performed for 8 hours.

After cooling, the sample recovered from the furnace was a red lump, which was crushed in a mortar and passed through a sieve with an opening of 75 μm.

The powder that passed through the sieve was washed with hydrochloric acid and water and dried to obtain the phosphor of Example 1.

(Confirmation of crystal structure)
The crystal structure of the obtained phosphor of Example 1 was confirmed by a powder X-ray diffraction pattern using CuKα rays using an X-ray diffraction device (Rigaku Co., Ltd., Ultima IV). As a result, in the powder X-ray diffraction pattern of the obtained phosphor of Example 1, a diffraction pattern identical to that of CaAlSiN ₃ crystal was observed, indicating that only a compound having the same crystal structure as the CaAlSiN ₃ crystal phase was obtained. I found out that there is.

(Quantitative analysis of Eu)
The Eu content in the obtained phosphor of Example 1 was determined using an ICP emission spectrometer (manufactured by Rigaku Co., Ltd., CIROS-120) after dissolving the phosphor using a pressure acid decomposition method. I analyzed it and found it. As a result, the Eu content in the phosphor of Example 1 was 1.61 wt%.

(Evaluation of absorption rate)
The absorption rate of the phosphor was measured as follows. First, a standard reflector (manufactured by Labsphere, CSRT-99-020, Spectralon) with a reflectance of 99% is attached to an integrating sphere, and a monochromatic light beam with a wavelength of 455 nm from an emitting light source (Xe lamp) is attached to the integrating sphere. Light was introduced using optical fibers. The excitation spectrum using this monochromatic light as an excitation source was measured using a spectrophotometer (manufactured by Otsuka Electronics Co., Ltd., MCPD-7000). At that time, the number of excitation light photons (Qex) was calculated from the spectrum in the wavelength range of 450 to 465 nm. Next, instead of the standard reflector, a phosphor filled with a smooth surface is set in the recessed cell, the fluorescence spectrum of the phosphor is measured, and the number of excitation reflected light photons (Qref) is calculated from the obtained spectral data. Calculated. From the two types of photon numbers obtained, 455 nm absorption rate a (=((Qex−Qref)/Qex)×100) was determined. Furthermore, the excitation spectrum and fluorescence spectrum using excitation light with a wavelength of 700 nm were measured in the same manner, and the number of excitation light photons (Q'ex) and the number of excitation reflected light photons (Q'ref) were calculated. At this time, the number of excitation light photons (Q'ex) was calculated from the spectrum in the wavelength range of 695 to 710 nm. From the two types of photon numbers obtained, the 700 nm absorption rate b (=((Q'ex-Q'ref)/Q'ex)×100) was determined. The phosphor of Example 1 had an absorption rate a of 96.4% at a wavelength of 455 nm and an absorption rate b of 4.6% at a wavelength of 700 nm.

(Evaluation of fluorescence intensity)
Fluorescence intensity was evaluated using a spectrofluorometer (manufactured by Hitachi High-Technologies, F-7000) calibrated with Rhodamine B and a secondary standard light source. Using the solid sample holder attached to the photometer, a fluorescence spectrum was determined at an excitation wavelength of 455 nm. As a result, the peak wavelength of the fluorescence spectrum emitted by the phosphor of Example 1 was 630 nm. Note that since the brightness of the phosphor varies depending on the measuring device and conditions, the value of the fluorescence intensity of Example 1 was set as 100% and was used as the evaluation standard for other Examples and Comparative Examples. In the present invention, if the fluorescence intensity value is 90% or more, it is determined that the brightness, which is the objective of the present invention, is satisfied.

The firing temperature, Eu content, fluorescence peak wavelength, 455 nm absorption rate a, 700 nm absorption rate b, the value of the difference a-b, and the emission intensity of the fluorescence spectrum of the phosphor of Example 1 are summarized in Table 1 shown below. .

(Example 5)
In Example 5, the same raw material powder as in Example 1 was used, and 62.1 g of Si ₃ N ₄ , 2.8 g of Ca ₃ N ₂ , 120.0 g of Sr ₃ N ₂ , 54.7 g of AlN, and Eu It was produced under the same conditions as Example 1 except that ₂ O ₃ was blended at a ratio of 10.3 g.

(Comparative example 1)
Comparative Example 1 used the same raw material powder as Example 1, including 64.7 g of Si ₃ N ₄ , 3.2 g of Ca ₃ N ₂ , 124.4 g of Sr ₃ N ₂ , 56.7 g of AlN, and Eu ₂ O ₃ was blended at a ratio of 1.0 g. Further, in the firing process, the temperature was raised to 1850°C after gas introduction, and the holding temperature was 1850°C, and firing was performed for 8 hours.

(Comparative example 2)
Comparative Example 2 used the same raw material powder as in Example 1, including 63.1 g of Si ₃ N ₄ , 8.7 g of Ca ₃ N ₂ , 108.6 g of Sr ₃ N ₂ , 55.3 g of AlN, and Eu. It was produced under the same conditions as Example 1 except that ₂ O ₃ was blended at a ratio of 14.3 g.

(Examples 2 to 4, Comparative Example 3)
In Examples 2 to 4, after the gas was introduced in the firing process, the temperature was raised to 1900 °C, 1850 °C, and 1750 °C, respectively, and the holding temperature was set to 1900 °C, 1850 °C, and 1750 °C, respectively, and firing was performed for 8 hours. Comparative Example 3 was produced under the same conditions as Example 1, except that the temperature was raised to 1650°C after gas introduction in the firing process, and the holding temperature was 1650°C and firing was performed for 8 hours.

When the crystal structures of the phosphors obtained in Examples 2 to 4 and Comparative Examples 1 to 3 were confirmed using an X-ray diffraction device, compounds having the same crystal structure as the CaAlSiN ₃ crystal phase were obtained in each case. That's what I found out. In addition, the Eu content, fluorescence peak wavelength, 455 nm absorption rate a, 700 nm absorption rate b, difference a-b, and emission intensity of the phosphors obtained in Examples 2 to 4 and Comparative Examples 1 to 3 were Measurements were made in the same manner as in 1, and the results are shown in Table 1. In addition, in Examples 1 to 4 in which the Eu source was added at the same blending ratio, the Eu content decreased as the firing temperature increased, because the amount volatilized as Eu ₂ O ₃ etc. during firing increased. This is thought to be due to a decrease in the Eu content in the resulting phosphor. This result confirms that the control of a-b is not determined only by the amount of Eu. In other words, the value of a-b referred to in this specification is an index that reflects the composition of the red phosphor as a product, including factors such as the degree of distortion of the crystal structure, the amount of foreign phases, the state of mixing with foreign phases, and the amount of impurities. It can also be said that That is, the red phosphor according to the embodiment of the present invention can be considered to have a different structure as a product from the red phosphor according to the prior art based on the value of ab.

From the results of Examples and Comparative Examples shown in Table 1, it can be seen that the red phosphor of the present invention in which a-b is defined within a specific range has relatively high fluorescence intensity.

The CaAlSiN ₃ -based phosphor of the present invention is excited by blue light and emits high-intensity red light, so it can be suitably used as a phosphor for white LEDs that use blue light as a light source, and can be used in lighting equipment, It can be suitably used for light emitting devices such as image display devices.

Claims (3)

General formula: MAlSiN ₃ (M is one or more elements selected from Ca and Sr), part of the M element is replaced with Eu element, and the main crystal phase has the same structure as the CaAlSiN ₃ crystal phase. 91.8 %≦a−b≦93.8%, where the absorption rate for excitation light with a wavelength of 455 nm is a% and the absorption rate for excitation light with a wavelength of 700 nm is b%. ,
A phosphor having an Eu content of 1.61 to 2.81 wt%. The phosphor according to claim 1, wherein the M element contains at least Sr. A light-emitting device comprising the phosphor according to claim 1 or 2 and a light-emitting element.